Determination of selected fate and aquatic toxicity characteristics of acrylic acid and a series of acrylic esters

Acrylic acid, methyl acrylate, ethyl acrylate, and butyl acrylate are commercially important and widely used materials. This paper reports the results of a series of fate and aquatic toxicity studies. The mobility in soil of acrylic acid and its esters ranged from 'medium' to 'very high'. Calculated bioconcentration factors ranged from 1 to 37, suggesting a low bioconcentration potential. Acrylic acid and methyl acrylate showed limited biodegradability in the five day biochemical oxygen demand (BOD5) test, while ethyl acrylate and butyl acrylate were degraded easily (77% and 56%, respectively). Using the OECD method 301D 28-d closed bottle test, degradability for acrylic acid was 81% at 28 days, while the acrylic esters ranged from 57% to 60%. Acrylic acid degraded rapidly to carbon dioxide in soil (t1/2 < 1 day). Toxicity tests were conducted using freshwater and marine fish, invertebrates, and algae. Acrylic acid effect concentrations for fish and invertebrates ranged from 27 to 236 mg/l. Effect concentrations (LC50 or EC50) for fish and invertebrates using methyl acrylate, ethyl acrylate, and butyl acrylate ranged from 1.1 to 8.2 mg/l. The chronic MATC for acrylic acid with Daphnia magna was 27 mg/l based on length and young produced per adult reproduction day and for ethyl acrylate was 0.29 mg/l based on both the reproductive and growth endpoints. Overall these studies show that acrylic acid and the acrylic esters studied can rapidly biodegrade, have a low potential for persistence or bioaccumulation in the environment, and have low to moderate toxicity.     

The solid-phase controls on the mobility of heavy metals at the Copper Cliff tailings area, Sudbury, Ontario, Canada

The Copper Cliff Tailings Disposal Area, located near Sudbury, Ontario, covers an area of approximately 2200 ha and constitutes more than 10% of the total area of all mine tailings in Canada. The area has been utilized since 1936, receiving sulphide-containing tailings from the Inco Sudbury operations. Field measurements of pore-gas oxygen and carbon dioxide in the vadose zone indicate that sulphide oxidation has progressed to depths of 1.6 m to 1.7 m within the tailings. The oxidation of sulphide minerals within the vadose zone, and the accompanying dissolution of carbonate and aluminosilicate minerals within these tailings releases SO₄, Fe(II) and other metals to the pore water. In the vadose and saturated zones, concentrations of Fe and Ni exceed 10100 mg/l and 2210 mg/l, respectively. These high concentrations of dissolved metals are attenuated by a series of precipitation, coprecipitation and adsorption reactions. The precipitation of secondary sulphate and hydroxide phases also create hardpan layers at or near the oxidation front. Geochemical modelling of the pore-water chemistry suggests that pH-buffering reactions are occurring within the shallow oxidized zones, and that secondary-phase precipitation is occurring at or near the underlying hardpan and transition zones. Mineralogical study of the tailings confirmed the presence of jarosite, gypsum and goethite within the shallow tailings, suggesting that these phases are controlling the dissolved concentrations of Fe, SO₄ and Ca. Extraction experiments conducted on the tailings solids indicate that the constituents contained in the water-soluble fraction of the shallow, weathered tailings are derived from the original pore water and the dissolution of highly soluble phases such as gypsum. The acid-leachable fraction of the weathered tailings accounts for up to 25% of the heavy metals, and the reducible fraction may contain up to 100% of the heavy metals within the shallow, weathered tailings. Based on the pore water profiles and the geochemistry of the tailings solids, a relative mobility scale of Fe=Mn=Ni=Co>Cd Zn>Cr=Pb>Cu can be determined.     

Chemical methods and phytoremediation of soil contaminated with heavy metals

The effects of chemical amendments (calcium carbonate (CC), steel sludge (SS) and furnace slag (FS)) on the growth and uptake of cadmium (Cd) by wetland rice, Chinese cabbage and wheat grown in a red soil contaminated with Cd were investigated using a pot experiment. The phytoremediation of heavy metal contaminated soil with vetiver grass was also studied in a field plot experiment. Results showed that treatments with CC, SS and FS decreased Cd uptake by wetland rice, Chinese cabbage and wheat by 23-95% compared with the unamended control. Among the three amendments, FS was the most efficient at suppressing Cd uptake by the plants, probably due to its higher content of available silicon (Si). The concentrations of zinc (Zn), lead (Pb) and Cd in the shoots of vetiver grass were 42-67%, 500-1200% and 120-260% higher in contaminated plots than in control, respectively. Cadmium accumulation by vetiver shoots was 218 g Cd/ha at a soil Cd concentration of 0.33 mg Cd/kg. It is suggested that heavy metal-contaminated soil could be remediated with a combination of chemical treatments and plants.     

Nitrogen oxides from waste incineration: control by selective non-catalytic reduction

An experimental study of the selective non-catalytic reduction (SNCR) process was carried out to determine the efficiency of NOx removal and NH3 mass balance, the NOx reducing reagent used. Experimental tests were conducted on a full-scale SNCR system installed in a hospital waste incineration plant. Anhydrous NH3 was injected at the boiler entrance for NOx removal. Ammonia was analyzed after each flue-gas treatment unit in order to establish its mass balance and NH3 slip in the stack gas was monitored as well. The effective fraction of NH3 for the thermal NOx reduction was calculated from measured values of injected and residual NH3. Results show that a NOx reduction efficiency in the range of 46.7-76.7% is possible at a NH3/NO molar ratio of 0.9-1.5. The fraction of NH3 used in NOx removal was found to decrease with rising NH3/NO molar ratio. The NH3 slip in the stack gas was very low, below permitted limits, even at the higher NH3 dosages used. No direct correlation was found between the NH3/NO molar ratio and the NH3 slip in the stack gas since the major part of the residual NH3 was converted into ammonium salts in the dry scrubbing reactor and subsequently collected in the fabric filter. Moreover, another fraction of NH3 was dissolved in the scrubbing liquor.     

Mechanisms of lead, copper, and zinc retention by phosphate rock

The solid-liquid interface reaction between phosphate rock (PR) and metals (Pb, Cu, and Zn) was studied. Phosphate rock has the highest affinity for Pb, followed by Cu and Zn, with sorption capacities of 138, 114, and 83.2 mmol/kg PR, respectively. In the Pb-Cu-Zn ternary system, competitive metal sorption occurred with sorption capacity reduction of 15.2%, 48.3%, and 75.6% for Pb, Cu, and Zn, respectively compared to the mono-metal systems. A fractional factorial design showed the interfering effect in the order of Pb>Cu>Zn. Desorption of Cu and Zn was sensitive to pH change, increasing with pH decline, whereas Pb desorption was decreased with a strongly acidic TCLP extracting solution (pH = 2.93). The greatest stability of Pb retention by PR can be attributed to the formation of insoluble fluoropyromorphite [Pb(10)(PO(4))(6)F(2)], which was primarily responsible for Pb immobilization (up to 78.3%), with less contribution from the surface adsorption or complexation (21.7%), compared to 74.5% for Cu and 95.7% for Zn. Solution pH reduction during metal retention and flow calorimetry analysis both supported the hypothesis of retention of Pb, Cu, and Zn by surface adsorption or complexation. Flow calorimetry indicated that Pb and Cu adsorption onto PR was exothermic, while Zn sorption was endothermic. Our research demonstrated that PR can effectively remove Pb from solutions, even in the presence of other heavy metals (e.g. Cu, Zn).     

A multi-process phytoremediation system for removal of polycyclic aromatic hydrocarbons from contaminated soils

To improve phytoremediation processes, multiple techniques that comprise different aspects of contaminant removal from soils have been combined. Using creosote as a test contaminant, a multi-process phytoremediation system composed of physical (volatilization), photochemical (photooxidation) and microbial remediation, and phytoremediation (plant-assisted remediation) processes was developed. The techniques applied to realize these processes were land-farming (aeration and light exposure), introduction of contaminant degrading bacteria, plant growth promoting rhizobacteria (PGPR), and plant growth of contaminant-tolerant tall fescue (Festuca arundinacea). Over a 4-month period, the average efficiency of removal of 16 priority PAHs by the multi-process remediation system was twice that of land-farming, 50% more than bioremediation alone, and 45% more than phytoremediation by itself. Importantly, the multi-process system was capable of removing most of the highly hydrophobic, soil-bound PAHs from soil. The key elements for successful phytoremediation were the use of plant species that have the ability to proliferate in the presence of high levels of contaminants and strains of PGPR that increase plant tolerance to contaminants and accelerate plant growth in heavily contaminated soils. The synergistic use of these approaches resulted in rapid and massive biomass accumulation of plant tissue in contaminated soil, putatively providing more active metabolic processes, leading to more rapid and more complete removal of PAHs.     

Co-injection of air and steam for the prevention of the downward migration of DNAPLs during steam enhanced extraction: an experimental evaluation of optimum injection ratio predictions

When steam is injected into soil containing a dense volatile non-aqueous phase liquid contaminant, the DNAPL vaporized within the heated soil region condenses and accumulates ahead of the steam condensation front. If enough DNAPL accumulates, gravitational forces can overcome trapping forces allowing the liquid contaminant to flow downward. By injecting air with steam, a portion of the DNAPL vapor remains suspended in equilibrium with the air, decreasing liquid contaminant accumulation ahead of the steam condensation front, and thus reducing the possibility of downward migration. In a previous work, a theoretical model was developed to predict the optimum injection ratio of air to steam that would eliminate accumulation of DNAPL ahead of the temperature front and thus minimize the potential for downward migration. In this work, the theoretical model is summarized, and an experiment is presented in order to evaluate the optimum injection ratio prediction. In the experiment, a two-dimensional water saturated sand pack is contaminated with a known mass of TCE (DNAPL). The system is then remediated by co-injecting air and steam at the predicted optimum injection ratio, calculated based on the average contaminant soil concentration in the sand pack. Results for the co-injection of air and steam are compared to results for the injection of pure steam or pure air. Injection at the predicted optimum injection ratio for a volumetric average NAPL saturation, reduced accumulation of the contaminant ahead of the condensation front by over 90%, as compared to steam injection alone. This indicates that the optimum injection ratio prediction is a valuable tool for limiting the spreading of DNAPL during steam-enhanced extraction. Injection at the optimum injection ratio resulted in earlier recovery of contaminant than for steam injection alone. Co-injection of steam and air is also shown to result in much higher recovery rates than air injection alone.     

Effect of surfactants at low concentrations on the sorption of atrazine by natural sediment.

A series of experiments were carried out to determine the effect of surfactants at low concentrations on the sorption of atrazine by natural sediments. With surfactant concentrations ranging from 0 to 20 mg/ L, anionic and cationic surfactants appreciably reduce the adsorption of atrazine, while nonionic surfactant decreases the adsorption of atrazine at concentrations equal to or less than 1 mg/L and increases adsorption at higher concentrations. Desorption of atrazine in the presence of different sodium dodecylbenzene sulfonate (SDBS) concentrations shows that a portion of the bound pesticide resists desorption in the SDBS free system. However, the addition of SDBS accelerates the desorption of atrazine. Furthermore, the nature of sediment and the contacting sequence of SDBS, at 10 mg/L, with the sediment, also influence the adsorption of atrazine. The conclusions in this study could be explained partially by the effect of the type and concentration of surfactants and the characteristics of sediments.